A high-temperature battery, and also a high-temperature electrolyzer, have to be supplied with sufficient heat for providing a suitable operating temperature. Therefore, in a high-temperature battery as described in DE 10 2009 057 720.3, for example, heating of the battery cell up to a temperature level of at least 700° C. is necessary in order to be able to ensure an efficient operation. Equally, high-temperature electrolyzers, as described in EP12163588, for example, are to be supplied with heat in order to be able to operate an efficient electrochemical gas separation plant. The efficiency of both devices is influenced significantly by the operating temperature which, for example, determines the necessary ion fluxes in the devices.
The necessary heat is made available in this case, at least partially, by a flow of hot air which is fed to the high-temperature battery or to the high-temperature electrolyzer. The temperature level of this hot air, however, does not have to achieve the operating temperature level of the high-temperature battery or of the high-temperature electrolyzer but should be high enough in order to be able to make a significant heat contribution. In the present case, thermally conditioned air, the temperature level of which lies above the ambient temperature level, is therefore to be understood by hot air. Within the scope of the present invention, a high-temperature battery, and also a high-temperature electrolyzer, is to have an operating temperature of at least 300° C., preferably of at least 650° C. In particular, the temperatures are to be high enough in order to be able to operate, according to design, a high-temperature battery or a high-temperature electrolyzer which work at least partially on the basis of a solid electrolyte fuel cell (SOFC). In this case, temperatures of at least 650° C. are typically required.
Comparable operating preconditions are known from the technical scope of high-temperature fuel cells which are designed as a solid electrolyte fuel cell (SOFC). Thus, it is described in US 2004/0013913 A1, for example, that such a high-temperature fuel cell is supplied with heated air by means of an air piping system. The heating is carried out in this case so that the air which is fed to the high-temperature fuel cell is conditioned by means of a heat exchanger and a suitable heating device. The energy which is released from the heat exchanger to the air is partially extracted from a backflow pipe which discharges used air from the high-temperature fuel cell and feeds it to the heat exchanger. Depending on the amount of hot air which is discharged from the high-temperature fuel cell, a greater or lesser quantity of heat can therefore be fed again, by means of the heat exchanger, in a thermal recirculation circuit to the high-temperature fuel cell, as a result of which the overall heat loss can be minimized. Moreover, with increased recirculation the temperature gradient across the fuel cell can be reduced. The controlling of the overall quantity of thermal energy which is fed to the air flow is undertaken by a control system which determines the additional external heat input in order to be able to ultimately supply the high-temperature fuel cell with sufficient overall heat.
Since, however, unlike in the case of a high-temperature fuel cell, the operation of a high-temperature battery or of a high-temperature electrolyzer is typically carried out under different and temporally variable load- and working conditions, a temporally varying supply of the high-temperature battery or of the high-temperature electrolyzer with thermal heat is necessary. A process step absorbing electric energy is typically conducted endothermally in the case of a high-temperature electrolyzer, which necessitates a feed of heat. In contrast to this, a process step releasing chemical energy is typically conducted exothermally. If the operation of a high-temperature electrolyzer is now carried out in such a way that both types of operation are undertaken alternately, a varying supply with heat is necessary. Similarly, a high-temperature battery can be operated in two different working states, being an electric energy-absorbing and endothermal charging state and also an electric energy-releasing and exothermal discharging state. Consequently, a varying supply with heat is also necessary here if both working states are selected alternately with each other.
Furthermore, high-temperature batteries or high-temperature electrolyzers can be provided for absorbing surplus energy from renewable, fluctuating energy sources (wind energy, solar energy). This leads to a continuous change of the power to be absorbed and therefore also to changes in their working state.
Different working states, however, typically also require mass flows in the air supply which differ from each other. As a result, the operation of a high-temperature battery or of a high-temperature electrolyzer differs in principle, however, from that of a high-temperature fuel cell which typically has only a single defined working state.
If a high-temperature battery or a high-temperature electrolyzer has to be supplied with temporally varying mass flows of air, it is shown that the thermal conditioning, as described in US 2994/0013913 A1, cannot be operated with adequate efficiency. Under such circumstances, there may specifically be a requirement for a higher thermal heat input into the air flow which can be covered only by providing large quantities of thermal energy by means of an external heat source. The exclusively thermal injection of heat from the backflow pipe proves energetically to be of insufficient advantage in this case. Moreover, the control speed can prove to be insufficient for the rapid heating of large air flows.
Consequently, it is technically necessary to propose a control system for temperature control of a high-temperature battery which is supplied with hot air via a piping system, or of a high-temperature electrolyzer which is supplied with hot air via an air piping system, which avoids the disadvantages from the prior art. In particular, an energy-efficient operation is also to be enabled in the case of varying mass flows in the air supply. Furthermore, the supply of a high-temperature battery or of a high-temperature electrolyzer with a temporally varying mass flow is to be enabled, wherein the thermal conditioning of this mass flow is carried out in a comparatively energy-efficient manner.